Synology seems to further favor their “own” (re-labeled, Toshiba- and Seagate-produced) drives instead of the numerous other once which still appear in the official HCL like we knew it over the years, starting with the 25-Plus-models.
https://www.heise.de/en/news/Synology-restricts-choice-of-hard-disks-for-new-Plus-NAS-10356960.html
Filesystem is either EXT4 or BTRFS, but the partitioning and redundancy from their SHR system is a combination of RAID1/5 and LVM.